Propellant chamber means



Un ed States PROPELLANT CHAMBER MEANS Henry H. Mohaupt, Fort Worth, Tex.

Application October 8, 1954, Serial No. 461,272

7 Claims. (Cl. 89-1) producing or potential producing earth formations 'is increased. Such process includes the firing into the formation of a missile possessed of extremelyhigh kinetic.

energy, such missile beingfired from a tool barrel and prinicpally accelerating in a direction along the axis of the well bore, i. e., the barrel extends vertically down the well bore and the missile is fired therethrough. An application entitled Penetrating and Fracturing Tool and filed January 25, 1954, in the name of Henry H. Mohaupt .and having Serial No. 405,823 describes and claims such a process wherein directing means is used at the end of the tool barrel to direct the missile into the formation.

Additional uses for a .tool of the general nature described in the aforesaid application have been found,such

uses for example comprising the destruction of objects.

within the well, such as tools dropped thereinto and the like, and the drilling of additional well bore by firing the missile through strata relatively impervious to ordinary drilling bits. In these applications the penetrating tool does not normally use missile-directing means. a Y

The aforesaid tool is characterized by the presence of a long barrel, a relatively massive missile and an exceedingly large powder charge which missile, as stated above, upon being fired possesses tremendous kinetic energy.- Inasmuch as strict limitations are imposed upon the design of such a tool by virtue of the relatively small well bore diameters in which the tool must be used, the capacity of the propellant chambers able to accommodate the necessarily large propellant volumes can only be achieved by a relative increase in the length of the propellant chamber as compared to the possible increase in propellant chamber diameter.

Workable maximum ratios of chamber lengthto diameter, however, have long been established and adhered to in the propellant art, as for example, in firearms. These ratios have not materially changed since the introduction of. smokeless powder and are of the order of 5 to 1. On the other hand in practicing the aforesaid process in oil wells ordinarily restricted in diameter to about 7 inches or considerably less, in order to impart the necessary kineticenergy to the missile fired, the ratio of chamber length to diameter must frequently be. as large as 30' to l orcon'siderably higher.

Unfortunately, investigation of the behavior of'p'ropelr lants in propellant chambers having high ratios of length to diameter demonstrates that conventional propellant practice will not permit tool design compatible with the aforedescribed process in wells. As is well known the limitations imposed upon -propellant chamber design by material strengths, shapes, thicknesses, and the like, make it mandatory that erratic or fluctuating, and particularly high peak chamber pressures resulting from the burning of the propellant charges within the chambers be avoided.

Otherwise, chamber failure must and does occur. Thus in tests conducted utilizing-standard propellant practice and tools comprising barrels and standard propellant chambers, it has been determined that chamber pressures generated do not vary greatly as chamber length is increased from approximately one diameter to approximately five diameters. In these tests the weight of propellant is of course increased while the loading density kept constant and normal.

Further lengthening of the chamber beyond ratios of 5 to 1, however, appears first to increase the pressure in the entire ,chambenbut unpredictably such condition may" suddenly yield to high magnitude localized pressures. For

example, it appears that given a chamber length to dia meter: ratio of 9 to 1, the strongest steel chambers are swelled either. at the ignition end 'or' at the front end adjacent to the missile, pressures in excess of 100,000 lbs. (p.s.i.) being registered at these points. As the aforesaid ratio is further increased complete bursting of the cham:

ber frequently takes place. A careful analysis of the resulting fragments shows that failure occurs at one or the otheror both .ends of-thechamber and thereby demonstrates that the peak uncontrollable pressures occur at I the ends of the chamber.

Furthermore, decreasing of the loading density of the propellant doesnot overcome, contrary to expectations,

the erratic pressure conditions mentioned but seems to aggravate such conditions, it appearing that the disruptive effects at even the low loading'densities arequite similar to. the effects obtained at the higher normal loading densities. 9

While the explanation for the aforesaid phenomena must of course be theoretical, it appears'thatthe excessive and destructive pressures in propellant chambers having abnormally high'lehgth to diameter ratios are caused by the acceleration of the propellant particles themselves and theirconsequent compression or impact against the ends of the chambers. This impact and resulting high compression of the propellant results in a vastly increased burning rate in the affected portions of the propellant and creates uncontrollable pressures at those points. These erratic pressures are not characteristic of, any particular type or composition of propellant but occur in all types. Explanation of the fact that disruptive pressures have been found adjacent the igniting point of the propellant as distinguished from the opposite end of the chamber apparently resides in the fact of oscillation or rebound.

' The basic cause, therefore, of the conditions described above may be theoretically summarized to the effect that flame propagation, the mode of combustion inherent and As previously stated, limitations imposed by. well di-- ameters severely limit. the permissiblediameter 'of .the tools used in the subject process, it being of course necesary to provide adequate clearance between the tool and the cased or uncased well bore. At thesame time-in order to impart sufiicient kinetic energy to the missile to accomplish its purpose, propellant charges must be used which cannot be encompassed within propellant chambers at the one time adhering to diameterlimitations imposed by the well bore and at the same time having the required volumetric capacities necessitated by the charge.

F9? tee l a arg im f wsl ar .PFQYi 1 with Patented Feb. 2, 1960 a casing having a /1." outsidev diameter and 4.9,"v inside diameter. This necessitates a tool having an outside diameter of not substantially greater than 4 and indeed in many cases, such as where heavy drilling mud. is used, the clearance must be. greater. It likewise-frequently desirable insuch a tool thata' missile: having; a diameter 0151.5" or greater be used.v In. order that the necessary severalhundredthousand ft-.-lbs.. of kinetic energy. be impartedv to the; missile; a propellant chamber of several feet oflength must. be used, but as isobvious' thataeven were-the diameter of the-chamber to beheld to 1 /2" the ratio of Chamber length to diameter will-bemanyfoldthat of. 5 to L. The wall thickness-of the propellant chamber.

cannot exceed about 1" at its thicker sections and may.

only. be about V2" at. its weaker sect-ions. Such'wall thickness allows no: safety margin whatsoever. for erratic or fluctuating,pressures-,-but in-v-iew of-Itheprinciplesabove set. forth the chamber. length. to diameter ratio willj ensure destructive pressures. Complicating, the: situation is; the. fact that given the slight clearance present in the well even a. slight swelling of the. toolzcannot be" tolerated because of the likely lodgingof the tool within the: well bore and consequent possible loss of the welL.

In the light of the conditions under which. the subject process must be practiced and the problem posed by the-theory set forth'above, the basisof the. instant invention, is. found. in theconceptionthat mass movement of the propellant. particles along the axis of the chamber must be avoided and with this in: mind. the-object-of this invention is. to provide novel propellant. chambernreans for use in: wells whereby erratic, fluctuating and high peak pressures are not developed in. the" chamber even though it. has an abnormally high lengthto diameter ratio. It. is also an object. of thisinvention to: provide a novel propellant charge: for use in accomplishing the aims of the invention. e

Other objects. and. advantages: of the instant: invention willbe apparent from the:followingtdescription;-

In. the drawings: t

Fig. lshows alongitudinal sectional view of propellant chamber. means. incorporating the instantv invention; and

Fig; 2 shows in'the same view adifierent embodiment of chamber propellant. means incorporating. the instant invention.

As statedv before, the basis" of" the instant invention is the'conception that extreme: axialacceleration of the charge particles: mustbe. avoided. This concept is: carried into: effect, first,. bymeans, comprising an annular expansion. space. within. the propellant chamber, and second, by means ensuring. a substantially:instantaneous ignitionover the entire length of the charge.

Referringtosthe embodiment of the invention shown by Fig. 1, it will beseen thata contact sub suspended from; the usual. conductor. cable not shownis threaded tozanadapterlZ, sealing rings-14 heing'provid'ed to pro videa safety sealbetween thesub and the adapter; 'Extending from. the conductor cable through bores in the sub" and adapter are ignition wires 16. Threaded tothe' adapter 12. andsealed" by sealing rings-18 isan elongated propellant chamber; 20. which propellant chamber'car ries an elongated propellant charge generally designated as: 22". and. which propellantchamber iswelded by the weld 24 to the barrel26; Itwill be not'ed-that-the'propellant chamber'ZO-and propellant charge 22 are shown as foreshortened, the-actualratios of length to-diameter of these elements being considerablyin excess of 10 to ll Amissile-28is' shown carried-by the-barrel 26, said mis'silei being -provided with gas-check means 30.

The' propellantjcharge22constitutes' a loader ordinary smokeless powder 32 cylindricall'yencompassed within a thin walled'frangible tube'34. The tube 34 need have merely-xthe strength to retain the powder in transport powder in place... The aforesaid plugs. 36 and. 38. may be composed of wood, aluminum, plastic or other frangible material. The ignition wires 16 extend into the powder 32 through a close-fitting bore 42 in the plug 36.

In operation the tool is lowered into the Well on the usual wire line to the firing zone, and the ignition wires 16 energized. By virtue of the extreme length to diameter ratio of the propellant chamber 20, were such chamber filled with powderv in. the usualmanner, propellant combustion would commence at the upper end of said chamber and burning Would be progressive downward'. The hot gases generated, however, would rush past and around the propellant particles towards the lower end of the propellant chamber and in so doing sweep with them unburned particles, thereby impacting and highly compressing the powder at the end of the chamber. As a result of this, the burning rate of the powder would greatly increase: and would. cause an excessive pressure peak, resulting in bulging, splitting; and even destruction of the chamberinthat vicinity. The consequence of this would not only be failure and destruction of the tool,.but additionally, damage to the well and casing and likely lodging. of the tool in the well.. g

It will be noted, however, thatthe diameter of the thinwalled. tube134-is considerably less than. the inside diam-s eter of the propellant chamber, providing thereby anannular expansion space. within the chamber; In operation,

' therefore, as soon as propellant ignition at. the; upper end and may, forexample, be composed of" aluminum. End

plugs 36 and38 arerutilizedin conjunction with thetube offthe tube is efiected, the tube bursts in that-vicinity and such bursting continues progressively'along the tube and within the propellant chamber as burning itself progresses. This aflfordscontinuous pressure release for the incandescent gases which are enabled to'rush. substantially unimpeded' into theexpansion annulus andproceed therealong parallel to the major: axis'of the chamberinsuch way' as not to sweep before'themthe propellant particles. The incandescent gases envelop the tube progressively forwardly" and laterally ignite the" propellant as it becomes exposed as a result of the downward progressive bursting ofthetube.

By this means axial acceleration and consequent impacting and compressing of the propellant particles at oneendofthe tube is avoided'and likewise excessive pressures are'substantiallyeliminated; Prop'ellingofthe missile 28 through thebarrel 26 therefore takes its'normal coursewithout damage to' propellant chamber, tool or well'.

Referring now to Fig. 2 wherein like parts are given like numericaldesignations, it will .be seen that rather than providing ignition wires, a'blasting cap 44 electrically explodedin the usual way is provided within a recess 46 in the contact sub 10, such blasting cap being adapted-to detonate the'detonati'ng fuse 48 which passes through a bore in the adapter 50. The detonating fuse, for ex ample maybe Primacord, marketed for many year's by the Ensign Bickford Company of Simsbury, Connecticut; 7 Such detonatingfuse 48 includesa relatively'smallcolumn 0f fast-acting detonating explosive encased in impregnated fabric, plastic, or the like, and the fuse extends through the close-fitting bore 42 in the plug36, lengthwise through the propellant'charge' 22, through at closefi tting. bore 52 in a retainer ring 54 which may also. be

composed of'wood, aluminum; or the like,.and isknotted or otherwise retained in a space 56 defined by'the ring 52and a plug 58', which again may be composed .of wood, aluminurn'or the'like. Centralizers 60 which may compn'se anmilarringsor spiders .made' of 'asbestoso'r similar material are provided which holdthe propellant charge 2 2"-ce'ntrally in the'powderchamber'ZO.

The. operationof the aforedescribed embodiment'of the invention issir'nilar to thatof the previously described embodiment, provided, however, thatdue to the speed'of propagation of'the detonating fuse, ignition of the powder 32' along the axis. of the propellant chamber'is. substan tially' instantan ous; said" pro agation ap roximating 20,000 ft. per second. This is greatly in excess of the propagation rate of the propellant and thus the entire length of the propellant charge is ignited before the unburned propellant particles may be axially accelerated due 'to the sweeping action of the incandescent gases.

It will be noted that an expansion annulus is provided in this embodiment of the invention as with the former embodiment, but it is to be understood that by virtue of the use of the detonating fuse, such annulus can under some conditions be dispensed with, as for example, if coarse, slow-burning powder be used under optimum tool and well conditions. On the other hand, it is recommended that the annulus be provided as a safety factor and to accommodate the tool to varying conditions of use. Thus, through utilization of the annulus relatively fasterburning, less coarse powder can be used. Similarly, detonating fuse failure can be protected against, for were the detonating fuse to effect propellant ignition at the upper end of the propellant charge but fail thereafter, lacking the annulus axial acceleration of the propellant particles would inevitably occur. Again, the effect of friction, barrel obstructions, and the like on the missile are diminished and varying weights of missiles may be used, an expedient which would be highly dangerous were the annulus safety factor disregarded. Again, provided the annulus is used, the tool may be operated in wells having extremely high temperatures, the annulus providing first, an insulation against auto-ignition of the propellant charge, and second, a space into which products of decomposition of the hot propellant may dissipate. In this latter regard, the provision of the propellant charge centralizer 60 will also be noted. Such centralizers provide the purpose of insulation of the charge. It will be appreciated that absent high temperature wells the centralizers may be dispensed with as is shown in the first embodiment of the invention. It will also be understood that in operating said first embodiment in high temperature wells, centralizers should be utilized.

It is apparent that other modifications may be devised incorporating the spirit and substance of the inventive features hereinabove disclosed, and it is understood that as to such modifications, applicant is entitled to the full breadth and scope of the appended claims.

I claim:

1. The combination with a barrel adapted for propelling a high energy missile of an elongated rigid propellant chamber having a length to diameter ratio of at least 9 to 1; an elongated propellant charge in said chamber and extending throughout the major portion of the length thereof; and firing means for said propellant, said firing means including a detonating fuse extending lengthwise through said propellant charge, said detonating fuse being adapted to ignite said propellant substantially instantaneously over its entire length.

2. The combination with a barrel adapted for propelling a high energy missile of an elongated rigid propellant chamber having a length to diameter ratio of at least 9 to 1; an elongated propellant charge in said chamber and extending throughout the major portion of the length thereof; and firing means for said propellant, said firing means including a detonating fuse extending lengthwise through said propellant charge having a propagation rate substantially higher than that of said propellant, said detonating fuse being adapted to ignite said propellant substantially instantaneously over its entire length.

3. The combination with a barrel adapted for propel:

ling a high energy missile of an elongated rigid propellant chamber having a length to diameter ratio of at least 9 to 1; an elongated propellant charge therein of less diameter than said chamber and extending throughout the major portion of the length thereof; and firing means for said propellant, said firing means including a detonating fuse extending lengthwise through said propellant charge, said detonating fuse being adapted to ignite said propellant substantially instantaneously over its entire length; and said propellant chamber defining an expansion annulus about said propellant charge.

4. The combination with a barrel adapted for propelling a high energy missile of an elongated rigid propellant chamber having a length to diameter ratio of at least 9 to 1; an elongated propellant charge in said chamber and extending throughout the major portion of the length thereof; and firing means for said propellant, said elongated propellant charge being of substantially less diameter than said chamber whereby said chamber defines an expansion annulus about said propellant charge.

5. The combination defined in claim 4 including centralizing means engaging said propellant and the walls of said chamber and holding said propellant axially centered in said chamber and spaced from the sides thereof.

6. The combination with a barrel adapted for propelling a high energy missile of an elongated rigid propellant chamber having a length to diameter ratio of at least-9 to 1; an elongated propellant charge therein; and firing means for said propellant, said propellant being of less diameter than said chamber and encompassed within a frangible tube, said propellant chamber defining an expansion annulus about said tube, and said firing means including a detonating fuse extending lengthwise through said tube, said detonating fuse being adapted to ignite said propellant substantially instantaneously over its entire length.

7. The combination with a barrel adapted for propelling a high energy missile of an elongated rigid propellant chamber having a length to diameter ratio of at least 9 to 1; an elongated, frangible, propellant-containing tube therein of less diameter than said chamber and extending throughout the major portion of the length thereof; centralizers positioning said tube within said chamber spaced from the walls thereof, said propellant chamber defining an expansion annulus about said tube; a propellant charge encompassed within said tube; and firing means for said propellant, said firing means including a detonating fuse extending lengthwise through said tube in igniting relation to said propellant, said detonating fuse being adapted to ignite said propellant substantially instantaneously over its entire length.

References Cited in the file of this patent UNITED STATES PATENTS 120,963 Gomez Nov. 14, 1871 671,708 Noble Apr. 9, 1901 868,876 Lheure Oct. 22, 1907 2,044,345 Barab June 16, 1936 2,568,078 McGahey Sept. 18, 1951 2,568,080 McGahey Sept. 18, 1951 2,696,259 Greene Dec. 7, 1954 2,775,200 Guenter Dec. 25, 1956 FOREIGN PATENTS 484,346 Great Britain May 4, 1938 592,092 Great Britain Sept. 8, 1947 

